In recent years, various technologies for creating encrypted information in which information on an URL or the like is coded or encrypted and for embedding the created encrypted information in a digital image or adding it to printed material have been developed (for example, see Patent Document 1). Furthermore, if encrypted information is embedded in a digital image (or added to printed material) without processing, it is impossible to determine the coordinates in an encrypted region on a digital image when the encrypted information is decoded. Accordingly, a technology for arranging markers at the four corners of the encrypted region at the time of the encryption has also been designed (see Patent Document 2).
Here, the conventional technology for arranging markers at the four corners of the encrypted region will be described. FIG. 29 is a schematic diagram illustrating a conventional technology. As illustrated in FIG. 29, with the conventional technology, when encrypted information is embedded in a digital image 10 to be encrypted, first, an encrypted region 11 is set (Step S10).
Subsequently, with the conventional technology, the encrypted information is embedded in the encrypted region 11 and markers 12 are arranged at the four corners of the encrypted region 11 (Step S11). Then, at the time of the decoding, the markers 12 arranged at the four corners of the encrypted region 11 are detected, the location of the encrypted region 11 is specified, and the encrypted information in the encrypted region 11 is decoded (Step S12).    Patent Document 1: Japanese Laid-open Patent Publication No. 07-254037    Patent Document 2: Japanese Laid-open Patent Publication No. 2008-301044
Because the markers 12 on a digital image 20 illustrated in FIG. 29 can be detected after printing, it is possible to decode an encrypted image regardless of whether it is printed material or a digital image. However, when an encryption process is performed, the markers 12 are overwritten on the digital image; therefore, there is a problem in that the markers 12 remain on a decoded digital image 30.
Furthermore, it is possible to perform two-dimensional coding on an encrypted region by using the technology disclosed in, for example, Japanese Laid-open Patent Publication No. 07-254037. However, at the time of the decoding, it is preferable to arrange markers that are used to specify the coordinates in an encrypted region. Accordingly, it is not possible to solve the problem of a marker remaining on the digital image.
The present invention has been conceived to solve the problems of the conventional technology described above, and an object thereof is to provide a marker creating program, a restoration program, a marker creating apparatus, a restoration apparatus, and a marker creating method that can completely restore an encrypted image without leaving a marker on the image.